Floating terminal for loading/offloading ships such as methane tankers

ABSTRACT

A floating terminal for loading/offloading cargo of ships such as methane tankers comprises an area for mooring ships and a submerged skirt to damp oscillation of the terminal to attenuate relative movement of the terminal and ships in the mooring area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a floating terminal forloading/offloading ships such as methane tankers.

2. Description of the Prior Art

Floating terminals for offshore mooring of ships such as methane tankersare known in the art.

These floating terminals are used to load/offload, and sometimes tostore, the cargo of these ships (generally liquefied natural gas orliquefied petroleum gas) using loading/offloading arms.

Floating terminals avoid these ships having to enter ports and thereforeeliminate the problems of space and safety that are inherent to the sizeand the nature, respectively, of the cargo of these ships.

To carry out loading/offloading operations, a ship must moor alongsidethe quay of a floating terminal, the loading/offloading manifolds orvalves of the ship being generally disposed half way along its length.

Until now, this kind of mooring could be envisaged only under relativelycalm sea conditions, to limit relative movement of the floating terminaland the ship and thus to carry out the loading/offloading operationsunder acceptable safety conditions. Limitation of relative movement ofthe floating terminal and the ship is also necessary when the floatingterminal is adapted to process hydrocarbons.

As a result of this, a floating terminal has in fact been available onlyintermittently, which has wasted a lot of time and therefore seriouslycompromised the return on the investment in the system.

An object of the present invention is to provide a floating terminalthat in particular avoids this major drawback.

SUMMARY OF THE INVENTION

This object of the invention is achieved with a floating terminal forloading/offloading cargo of ships such as methane tankers, the terminalcomprising an area for mooring ships and submerged skirt means disposedto damp oscillation of the terminal in order to attenuate relativemovement of the terminal and ships in the mooring area.

Because of the skirts for damping oscillation of the floating terminal,relative movement of the terminal and the ship may be significantlyreduced throughout mooring operations and during loading/offloading thecargo of the ships.

Thus the floating terminal many be used even when sea conditions arebad, which makes the terminal more profitable than in the prior art.

According to other features of the terminal of the invention:

-   -   the floating terminal comprises a submerged horizontal skirt;    -   the floating terminal comprises two submerged horizontal skirts        extending over at least a portion of the length of its lower        portion;    -   the floating terminal comprises a submerged vertical skirt;    -   the floating terminal comprises two submerged vertical skirts        extending over at least a portion of the length of its lower        portion;    -   the floating terminal comprises a skirt oriented at an angle        between the horizontal and the vertical and extending over at        least a portion of the length of its lower portion;    -   the floating terminal comprises means for orienting the floating        terminal relative to the swell, the wind, and the current;    -   the orientation means comprise fixed positioning means;    -   the fixed positioning means comprise a catenary anchoring        system;    -   the orientation means comprise mobile positioning means;    -   the mobile positioning means comprise a system chosen from the        group comprising turret systems and articulated arm systems;    -   the orientation means comprise displacement means;    -   the displacement means are chosen from the group comprising        thrusters and tugs;    -   the floating terminal comprises a swell damping chamber chosen        from the group comprising chambers on the upstream side of the        floating terminal relative to the direction of the swell and        chambers on the downstream side in that direction;    -   the damping chamber is of the perforated wall type;    -   the floating terminal comprises means for storing the cargo;    -   the floating terminal comprises plant chosen from the group        comprising lines and risers for importing/exporting the cargo,        loading/offloading arms for the cargo, means for treating the        cargo, crew quarters, maintenance areas, and control areas; and    -   the floating terminal is constructed from a material chosen from        the group comprising steel, reinforced concrete, and prestressed        concrete.

Other features and advantages of the invention will become apparent onreading the following description and examining the appended drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are plan views of a ship moored to a terminal according tothe invention connected to the sea bed by two variants of a positioningsystem.

FIGS. 3 to 8 are views along the shorter side of six variants of aterminal according to the invention.

FIG. 9 is a view along the longer side of a further variant of aterminal according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Refer now to FIG. 1, which represents a floating terminal 1 essentiallyformed of a floating caisson 3 moored to the sea bed by fixedpositioning means that may comprise a catenary anchorage system 5 a to 5d.

The floating caisson 3 may be made of steel and/or reinforced concreteand/or prestressed concrete.

It may support diverse plant, such as loading arms 7 a, 7 b, means forprocessing the cargo offloaded from or to be loaded onto the ships, crewquarters, maintenance and control areas (not shown), etc.

FIG. 1 also represents a ship 9 moored to the floating terminal 1 by anyappropriate means such as hawsers 11 a to 11 c.

The ship 9 may be a methane tanker, for example, for transportingliquefied natural gas (LNG) or liquefied petroleum gas (LPG).

In this case, the processing means supported by the floating caisson 3may comprise plant for liquefying/gasifying the cargo of the ship 9.

The caisson 3 comprises storage means (not shown) for storing the cargooffloaded from or to be loaded onto the ship 9.

It will be noted that the orientation of the floating terminal 1 to theprevalent direction D of the swell protects the ship 9 from the swell.

Refer now to FIG. 2, which represents a variant in which the floatingterminal 1 is connected to the seabed by a turret 13 known in the artand about which the caisson may pivot in a horizontal plane.

Instead, the turret 13 may be replaced by a soft yoke, i.e. anarticulated arm mounted on a jacket (metal truss structure) anchoragesystem (this variant is not shown).

These two variants constitute means for orienting the terminal 1appropriately relative to the direction D of the swell and relative tothe directions of the wind and the current.

In this case, displacement means 14 such as thrusters or tugs may beenvisaged for modifying the orientation of the caisson 3 by causing itto pivot about the vertical axis of the turret 13 or the soft yoke(articulated arm).

It will be noted that FIGS. 1 and 2 show loading/offloading arms 7 a, 7b that are disposed substantially halfway along the length of thefloating caisson 3.

This substantially corresponds to the position of the loading/offloadingmanifolds (valves) of methane tanker type ships, which are generallysituated halfway along their length.

Refer now to FIG. 3, in which it is seen that the immersed portion ofthe floating caisson 3 comprises horizontal skirts 15 a, 15 b extendingover at least a portion of its length.

The variant represented in FIG. 4 differs from that from the FIG. 3variant in that the skirts 17 a, 17 b are substantially vertical.

In the variant represented in FIG. 5, the caisson 3 is equipped withhorizontal skirts 15 a, 15 b and with vertical skirts 17 a, 17 b.

In another variant, not shown, the floating caisson 3 could be providedwith skirts oriented at an angle between the horizontal and thevertical.

Refer now to FIG. 6, in which it is seen that the floating caisson 3 maybe provided with a damping chamber 19 disposed on the side of thecaisson on which the swell impinges, i.e. on the upstream side of thefloating caisson 3 relative to the direction D of the swell.

A damping chamber of this kind is known in the art, and in particularfrom French patent FR 2 693 216, and may typically comprise an exteriorwall 21 provided with a plurality of regularly distributed orifices 23,as shown in FIG. 9.

This kind of wall is sometimes called a Jarlan wall.

In the variant represented in FIG. 7, the damping chamber 19 is on thedownstream side of the floating caisson 3 relative to the direction D ofthe swell.

In the variant represented in FIG. 8, the floating caisson 3 comprisesan upstream damping chamber 19 a and a downstream damping chamber 19 b.

The mode of operation and the advantages of the terminal according tothe invention follow directly from the foregoing description.

The ship 9 wishing to load or offload cargo moors alongside the quay ofthe floating terminal 3 on the side sheltered from the swell D (seeFIGS. 1 and 2).

The horizontal skirts 15 a, 15 b damp vertical oscillation of theterminal.

The vertical skirts 17 a, 17 b damp horizontal oscillation of theterminal.

Furthermore, the combination of these skirts limits the coefficient oftransmission of swell between the upstream and downstream sides of theterminal (the terms “upstream” and “downstream” being understood asmeaning with respect to the direction of the swell).

In the variant represented in FIG. 2, the orientation of the floatingterminal 1 may be modified at will to optimize the protection from theswell D, from the wind and from the current. The combination ofsubmerged skirts and means for controlling the orientation of theterminal is particularly advantageous.

All this radically reduces relative movement of the terminal and theship 9 when the ship is moving alongside and being moored to the caisson3 and while loading/offloading the cargo of the ship by means of thearms 7 a, 7 b.

Thus the floating terminal may be used even if the sea conditions arebad, which makes this terminal more profitable than in the prior art.

The cargo of the ship 9 may be stored and/or converted on the terminal 1or be sent directly from ship to land or vice-versa by means ofappropriate pipes.

Of course, the present invention is not limited to the embodimentdescribed and shown, which is provided by way of illustrative andnonlimiting example.

1. A floating terminal for loading/offloading cargo of ships such asmethane tankers, said terminal comprising an area for mooring said shipsand submerged skirt means disposed to damp oscillations of said terminalin order to attenuate relative movement of said terminal and ships insaid mooring area.
 2. The floating terminal claimed in claim 1comprising a submerged horizontal skirt.
 3. The floating terminalclaimed in claim 2 comprising two submerged horizontal skirts extendingover at least a portion of the length of its lower portion.
 4. Thefloating terminal claimed in claim 1 comprising a submerged verticalskirt.
 5. The floating terminal claimed in claim 4 comprising twosubmerged vertical skirts extending over at least a portion of thelength of its lower portion.
 6. The floating terminal claimed in claim 1comprising a skirt oriented at an angle between the horizontal and thevertical and extending over at least a portion of the length of itslower portion.
 7. The floating terminal claimed in claim 1 comprisingmeans for orienting said floating terminal relative to the swell, thewind, and the current.
 8. The floating terminal claimed in claim 7wherein said orientation means comprise fixed positioning means.
 9. Thefloating terminal claimed in claim 8 wherein said fixed positioningmeans comprise a catenary anchoring system.
 10. The floating terminalclaimed in claim 7 wherein said orientation means comprise mobilepositioning means.
 11. The floating terminal claimed in claim 10 whereinsaid mobile positioning means comprise a system chosen from the groupcomprising turret systems and articulated arm systems.
 12. The floatingterminal claimed in claim 10 wherein said orientation means comprisedisplacement means.
 13. The floating terminal claimed in claim 12wherein said displacement means are chosen from the group comprisingthrusters and tugs.
 14. The floating terminal claimed in claim 1comprising a swell damping chamber chosen from the group comprisingchambers on the upstream side of said floating terminal relative to thedirection of the swell and chambers on the downstream side in thatdirection.
 15. The floating terminal claimed in claim 14 wherein saiddamping chamber is of the perforated wall type.
 16. The floatingterminal claimed in claim 1 comprising means for storing said cargo. 17.The floating terminal claimed in claim 1 comprising plant chosen fromthe group comprising lines and risers for importing/exporting saidcargo, loading/offloading arms for said cargo, means for treating saidcargo, crew quarters, maintenance areas, and control areas.
 18. Thefloating terminal claimed in claim 1 constructed from a material chosenfrom the group comprising steel, reinforced concrete, and prestressedconcrete.